Method of making woven metallic web structures



Jam-1 1969 J. E. HECKETHORN 3,420,218

METHOD OF MAKING WOVEN METALLIC WEB STRUCTURES Original Filed Aug. 3,1965 Sheet of 5 '18 1%, i-1. OR, JOHN 5 HEcKErHo/a/v BY wit/w, ywa fku/saa ATTORNEY-5 n 7 1969 J. E. HECKETHORN 3,42

METHOD OF MAKING WOVEN METALLIC WEB STRUCTURES Original Filed Aug. 5,1965 Sheet 2 0r 3 '5 1s ac Lb F/a/U 1 6.// l/ ATTORNEYS United StatesPatent 3,420,278 METHOD OF MAKING WOVEN METALLIC WEB STRUCTURES John E.Heckethorn, Dyersburg, Tenn., assignor to Heckethorn Manufacturing (30.,Dyersburg, Tenn., a corporation of Colorado Original application Aug. 3,1965, Ser. No. 476,866, now Patent No. 3,372,406, dated Mar. 12, 1968.Divided and this application Mar. 30, 1967, Ser. No. 627,151 US. Cl.140-24 5 Claims Int. Cl. B21f 27/02; B21f 7/00; B23p /12 ABSTRACT OF THEDISCLOSURE Intertwisting the projecting ends of adjacent interwoundcomponent coils of a low-to-medium carbon hard-drawn steel meshstructure; the intertwisting being applied at first with a long pitchresulting in a gentle Working of the metal and with progressivelyreduced pitch until at the end of the twisting operation the turns ofthe wire ends are fully tightened and ready for bending about a stiffmarginal frame Without crystallizing or over-stressing the wires.

This application is a division of my co-pending application Ser. No.476,866, filed Aug. 3, 1965, now Patent No. 3,372,406, granted Mar. 12,1968.

The invention disclosed and claimed herein relates to improvements inventilated seat cushion structures of the general type exemplified in myUS. Patent No. 3,103,- 671 of Sept. 17, 1963.

More particularly the invention relates to improvements in the springpad constituting the internal structure of such a ventilated cushion.

In ventilated cushions of the type here involved, the spring pad,consisting of convoluted wire assembled within a substantially rigidmarginal frame, is housed within a porous air-permeable cover orenvelope to provide an air space permitting comparatively freecirculation of air between the body of a user and the supporting seatstructure on or against which the cushion rests. As is well known, thewire coils, in addition to engaging and supporting the body of the userto provide an air space therebeneath, act as heat exchangers between theusers body and the circulating air within or passing through the airspace.

In many of the prior seat cushion pad structures it has been customaryto bend or hook free ends of the wires forming the coils of the innerstructure around a stiff marginal wire frame in completing theconstruction. However, the strength and set of these end portions hasbeen found to be insufficient to prevent them from unhooking or becomingloosened, thereby detracting seriously from the strength of theconnection, the stability of the shape of the structure, and theinsurance that the partially unwound and loosened ends do not form barbswhich would endanger the surrounding fabric envelope of the cushion, theseating surface, or the body of the user.

It is therefore one of the primary objects of the invention to eliminatesuch difficulties by the provision of a novel and improved pad structureand method of making and assembling such pad structure. Thosedifiiculties, and the need for much tedious hand work in the assemblingprocess, have been obviated by the improved coil end and frame wireconnections disclosed herein.

These improvements include the provision of a proper kind of low ormedium carbon hand-drawn steel wire and processing it (either before orduring the assembling thereof) to give it the required strength toprevent unwinding or loosening; intertwisting properly the individualwires of adjacent coils; accurately and precisely severing hce theresulting twisted ends so that they will be substantially co-terminousand free of barbs or sharp projections; providing a structure which canbe manufactured for the most part mechanically, dispensing with some ofthe hand labor previously required; providing increased crush resistanceas compared with prior pads while at the same time permitting relativevertical sliding movement between certain of the coil convolutions tobetter conform to the contacting surfaces in use.

Thus, the novel cushion in its entirety, possesses improved comfort anddurability and the efliciency of the inner spring pad as a heat exchangeunit between the users body and the atmosphere is enhanced. And all thiswith a minimum expenditure of wire.

More particularly, the invention involves a choice of ways to render theintertwisted coil ends sufliciently strong to permanently maintain theirfirm hooked relationship with the stiff wire frame, and this involvesways to prevent the embrittlement of these wire ends. One processcomprises annealing at relatively hard wire to render it easier to twistWithout embrittlement or crystallizing, the temper and hardness beingsufliciently restored by the twisting operation so that when the twistedends are bent around the frame wire the hooks thus formed will take apermanent set, and have sufiicient rigidity to strongly retain theirshape so as to resist disconnection or loosening from the frame.However, I have also discovered that the annealing step may be dispensedwith in a preferred construction which involves the use of the harddrawn low or medium carbon steel, the twisting being accomplished in apeculiar novel progressive fashion to obviate the expected deleteriousembrittlement.

As will be apparent, the heat exchanging efliciency of such a spring padwill depend in part on the area of its heat exchanging surface in closeproximity to the body of the user and on the freedom with which aircirculation is permitted through the spring pad.

In the device of my prior Patent 3,103,671, it was proposed to flattenthe coil springs to an approximately oval configuration, but it has beenfound that such flattening of the springs has the effect of partiallycrushing them in such a way as to decrease the radius of curvature ofthe laterally opposed sectors of the individual spring coils, while atthe same time increasing the pitch angles of these sectors, therebyreducing their resistance to further crushing and also the flattening ofthe coils generates a torquing and distortion action of the coils. Also,in a number of prior constructions, the gradual flattening or collapsingof the coils over an extended period of use has resulted in soconstricting the air passages within the pad as to ubstantially impairthe air circulation.

In the case of the present invention, however, the spring coils areformed of as nearly rectangular configuration as is practical, havingdue regard to the permissible minimum radii to which the selected Wiremay be formed without annealing so that, in the resulting coils, eachconvolution of the spring is defined by comparatively long andapproximately rectilinear parallel reaches extending in substantiallycontinuous diagonal rows, avoiding any tendency to roll, to comfortablysupport the user, and thus dispose 1a proportionately greater length ofthe coil in heat conducting relationship with the body of the user.These rows diagonally cross the longitudinally and laterally disposedstrands of the cover fabric to thus support same with a minimum of wearand without penetration between adjoining strands.

These reaches are interconnected :at their ends by relatively spaced andsubstantially rectilinear connecting or supporting reaches extendingpredominately perpendicularly to the longer lateral reaches which theyinterconnect. In accordance with an important aspect of the invention,the short connecting reaches may be of minimum pitch or inclination, andyet the comparatively long lateral reaches may be widely spaced betweenadjoining convolutions of a given coil. This results in unusually highstrength and crush resistance even with the resulting wider spacingbetween adjoining convolutions of a coil, and a substantial reduction inthe total length of wire required. Also increased comfort to the userwill result. Due to the predominately perpendicular disposition andrectilinear shape of the respective supporting reaches, they willobviously provide superior resistance to crushing of the spring pad ascontrasted to the generally sharply or cylin drically curvedcorresponding portions of earlier spring coils employed for the samepurpose. Furthermore, these connecting reaches of adjoining coils crossand engage each other midway of the thickness of the structure to thusmore than double the strength at these point and brace each otheragainst lateral deflection, thereby contributing materially to the crushresistance of the entire spring pad.

Because of the parallelogram shape, in plan defined by opposing portionsof interlocked coils, an important contribution is made to the abilityof the spring pad to resist lateral deformation in the plane of the pad.It will be apparent that the interconnected parallelograms defined byadjoining horizontal spring reaches will interact in such a Way that alongitudinal force tending to compress or lengthen the pad will resultin a tendency toward deformation of the parallelograms, and thus betransmitted transversely to and through the parallelogram formation tothe frame, and be resisted both by the frame and the spring coils. Thus,the general shape of the frame is maintained against deformation.

The accompanying drawing and following detailed description areexemplary only, but will serve to disclose what is presentlycontemplated as the best modes known to me of practicing the invention.This of course will involve details which may be omitted or changed inways which will be obvious to those skilled in the art, withoutdeparting from the invention.

In the accompanying drawings:

FIGURE 1 is a view in perspective of .a ventilated seat cushionembodying the principles of the present invention, portions of thecovering material being broken away to reveal the interior wire padstructure;

FIGURE 2 is an enlarged fragmentary view in cross section taken on line2-2 of FIGURE 1; and showing certain marginal connecting features of theinner pad;

FIGURE 3 is a similar view but with the covering omitted and showing themanner of bending the twisted wire ends around the peripheral frame ofthe pad, the view being taken approximately on line 33 of FIGURE 4;

FIGURE 4 is a fragmented condensed plan view of the novel pad in itssubstantially completed form ready to be inserted into the coveringstructure of the seat cushion;

FIGURES 5, 6 and 7 are fragmentary transverse strips of the wire meshstructure showing successive stages of the cutting, twisting, trimming,and wrapping of the adjacent ends of the coils comprising the meshstructure; and leading up to the substantially completed pad structureof FIGURE 3;

FIGURES 8 and 9 are fragmentary views of a pair of twisted wire coilends suggesting the procedure and effect of the novel graduated stressmethod of twisting employed;

FIGURE 10 is a fragmentary sectional view through a single spring coilof the pad structure, as taken approximately on line 1010 of FIGURE 4,the broken rectangular outline suggesting the approximate cross-sectionof a blade or mandrel on which the coil was originally formed;

FIGURE 11 is a fragmentary sectional view taken on line 1111 of FIGURE 4and showing the approximate relative angular positions of the shortervertical reaches of the coil convolutions in an unstressed pad;

FIGURE 12 is a similar view of the same crossover junction as whenuneven pressure is applied to areas of the pad in the use of thecushion, and taken approximately on line 1313 of FIGURE 4; and

FIGURE 13 is a fragmentary vertical sectional View illustrating therelative vertical displacement of adjacent coils under varying stress inuse.

Referring now in detail to the accompanying drawings, in FIGURE 1 at 10there is illustrated a complete ventilated cushion structure of the typesuch as commonly employed on the seats of automobiles, office chairs andthe like, and including both a seat portion 11 adapted for positioningfor instance on a chair seat or on the seat of an automobile, and a backportion 12 adapted to overlie the back or back rest portion of the seat.The two portions 11 and 12 are of similar construction comprising springwire pads or assemblies 15 enclosed within a porous envelope or coversuggested generally at 16. Referring to FIGURE 2 in conjunction withFIGURE 1, it will be apparent that such cover is defined by opposedupper and lower sections 16A and 16B of loosely woven airpermeablefabric of generally rectangular configuration disposed on opposite sidesof the spring pads 15.

The marginal edges of these fabric layers 16 are sewed together andbound around their margins, as at 20. Preferably also a line or lines ofstitching 22 interconnects the two fabric layers of covering 16 betweenthe adjoining edges of the respective spring pads 15 and generallycoincident with the fold line defined between the two such pads whenoperatively positioned as in FIGURE 1. Thus the pads are properlypositioned and retained within the envelope 16 defined by the fabriclayers all in accordance with conventional practice.

It will be readily apparent that structures in accordance with theinvention may incorporate either a greater or lesser number of springpads than here illustrated and that the specific structure of the coveror envelope 16 is inconsequential, it being of importance only that suchenvelope shall be sufficiently air-permeable to permit the free entryand escape of air into and from the cushion for heat exchanging contactwith the spring pads 15 and with the clothing of the occupant of theseat.

Each of the spring pads 15 comprises a generally rigid rectangularmarginal frame 24 which is here shown in FIGURE 4 as formed inconventional manner from a length of relatively heavy and stiff wire,the ends of which are brought into abutting relation and secured thereinby a conventional connecting sleeve or ferrule 25 as in my earlierpatent, 3,103,671. The mesh or webbing comprising the greater area ofthe pads comprises wire coils 28 which are of uniform length and width,preferably though not necessarily extending from front to rear of theseat cushion. The laterally adjacent convolutions of adjoining springcoils 28 are interlocked in known manner, as suggested in FIGURES 11, 12and 13, while the coil convolutions at the lateral extremities of thecoil spring assembly thus provided are looped around longitudinallyopposed parallel reaches of the marginal frame 24 in a unique manner tobe later described.

The extremities of the respective spring coils 28 are connected to eachother in pairs, whereby to assist in maintaining the desiredrelationship and positioning of the several coils in the assemblythereof, and also are connected to the longitudinally opposed sectionsof the frame 24.

As has been mentioned earlier, it is desirable to interconnect or unitethe extremities of adjoining spring coils and also to firmly connectthese to the marginal frame 24, and the specific means for accomplishingthese connections, as well as the particular shape of the individualcoils and their specific relationships, constitute important features ofthe invention. The difficulty of achieving this in a manner to providefirm permanent inter-connections of the coil extremities to each otherand to the frame presented a formidable problem, as long recognized inthe art, this due to the known difiiculty of efficiently, properly, andaccurately positioning the coils and securely attaching the numerousindividual coil ends in a manner to eliminate the tendency to becomeunhooked from the frame and to prevent the formation of projecting endsforming barbs likely to snag or tear the envelope or covering fabric,the seat itself, or the clothing or body of the user.

Now, it was recognized that the strength of a single wire of rathersmall diameter is quite limited, and a hooked end of such a wire wouldhave very little holding power in forming a connection with the frame.It is for this reason I provide pairs of intertwisted coil ends forforming the hooked connections, and this involves certain problems inrelation to both rendering the wire ends sufiiciently pliable ormalleable for intertwining or intertwisting, and also giving the twistedends suflicient strength, rigidity, and holding power to make apermanent connection when bent around the frame wire, and withoutembrittlement. Certain solutions of these problems provided by thepresent invention will be described in detail following reference to thestructural features of the product as shown more particularly in FIGURES4 to 7 inclusive.

First, it may be stated that the individual coils 28 are formedpreferably by winding a wire of the desired properties around a rotatingblade or mandrel of approximately rectangular cross section, assuggested by broken lines at 128 in FIGURE 10, and the resultingsuccessive lengths of coiled wire, having the configuration shown inFIGURES 4 and 10, are threaded into the convolutions of the nextpreceding coil and thus the mesh or webbing of the pad is formed.

The conditions of winding on the mandrel, including the hardness of thewire stock, will result in a convolution shape somewhat like that shownin FIGURE 10, wherein the longer reaches 28' and the shorter reaches 28"are both bowed very slightly but not enough to nullify the descriptionof the outline of the convolutions as substantially rectangular, asopposed to the ovate configuration of many prior art coils.

Thus, it will be understood that a further important feature of theinvention consists in the specific shape and arrangement of each of thespring coils to provide maximum contact area with respect to the user,and maximum resistance to crushing, while requiring but a minimumexpenditure of wire for its construction.

Referring again particularly to FIGURES 2, 3 and 10 of the drawings, itwill be noted that while each convolution of a spring coil 28 is ofgenerally rectangular configuration or cross section, including thegenerally rectilinear side reaches 28' and end or vertical reaches 28",these reaches are interconnected to each other by bends defining thecorners of the substantial rectangle and which are as sharp as canpractically be produced, having due regard to the limitations inherentin the wire from which the coils are formed. The general arrangement istherefore such that the ends or connecting reaches 28" extend generallyrectilinearly between the planes of the opposed side reaches 28 and arepredominantly perpendicular to such planes. Furthermore, the connectingreaches 28" have small pitch angles. They are thus adapted toeffectually resist the crushing force imposed upon them by the weight ofthe user and thereby to maintain within the cushion structure throughoutits entire life an unobstructed or unimpeded air space permittingefiicient flow of air therethrough for heat exchange purposes.

On the other hand, the greater portion of the pitch angle of eachconvolution is comprised by its comparatively longer lateral orhorizontal reaches 28. These reaches thus extend diagonally to the axesof the coils and are parallel, so as to extend as a series of paralleldiagonal lines completely across the faces of the spring pad, anddiagonally to the longitudinally and laterally disposed fabric strandsof the porous cover. The possibility of penetration between strands ofthe cover is thus decreased, while comfort and durability of the cushionare increased accordingly. The coil configurations thus described areclearly shown in FIGURE 4 of the drawings as well as other figures.

It will be clearly understood thus that this interengaged coil meshstructure sufficiently approximates the truly rectangular concept so asto substantially achieve the benefits of great strength appurtenantthereto and yielding substantial improvements in crushing resistanceover previous structures of this description. The very slightly arcuatereaches of the coils 28 provide improved seating comfort and coilposition as compared to a completely accurate rectangular configuration.In previous socalled flattened coil structures, the coils with acircular cross-section are arcuately bent during the flattening processand therefore can offer no substantial compressive strength inresistance to crushing forces, and further bending of these alreadyarcuately bent sections is likely.

By virtue of the present invention it will be further apparent that thegenerally rectilinear lateral reaches 28' of the respective convolutionsadapted for supporting and heat conductive relationship with the body ofthe user represent a considerable larger proportion of the total coillength than is available in conventional rounded coil structures,thereby providing increased heat transfer qualities as well as improvedcomfort.

The interengagement of the coils 28 at the crossing points of theadjacent vertical reaches 28", as well as the substantially rectangularconfiguration provides a web or mesh constituting a pad insert for seatcushions in which the crush resistance is greatly enhanced. In fact, ithas been found by actual test that the structure formed in accordancewith the invention achieves a markedly greater crush resistance than isattainable in a conventional inner structure employing an equivalentamount of the same size and type of wire. In tests run by a qualifiedtesting laboratory, using hard-drawn wire of 0.038 inch in diameter, acrush resistance of 35.58 lbs. per square inch was obtained in astructure provided by the present invention, as compared to less than 16lbs. per square inch using an equivalent amount of wire of the same sizeand type in a conventional parallel coil arrangement such as is employedin my prior Patent No. 3,103,671, and as disclosed in the Crane PatentNo. 2,801,681.

Such tests also established that a substantially optimum included angleas indicated at a in FIGURE 11 of the drawings between the relativelycrossed end reaches 28" of adjoining coils, is one which is somewhatless than say 30. This would mean an angle of approximatelyl5 with thevertical as indicated at b. With the connecting portions so inclined andwith wire of the size and type above mentioned, a crush resistance inexcess of 35 pounds per square inch was attained. As this angle wasincreased, this crush resistance dropped somewhat. For instance, thestrength of the structure using the identical type of wire dropped to 30pounds per square inch when the included angle a between the adjacentconnecting reaches 28 was increased to 45. Widening the included anglebeyond 50 rendered the resistance too low for satisfactory use.

The arrangement of coils in accordance with the in vention, as shown inFIGURES 1 and 4, for instance, results in the provision of diagonallyextending parallel rows of upper and lower or relatively spaced wirereaches 28', with the ends of adjoining reaches in each row insubstantially overlapping relation and in such close proximity as tohave the effect of a continuous diagonal rectilinear support. It will benoted that the strands of the fabric 10, as shown fragmentarily inFIGURE 1, extend longitudinally and transversely respectively, whereasthe rows of reaches 28' extend diagonally and thus contact the fabric 10on a bias throughout the length of each row of diagonal reaches 28'.These very slightly curved reaches do not tend to project between thejoining fabric strands or cut through the strands as occurs inconventional parallel coil structures. This results in greaterdurability and greater comfort to the user than were heretoforeobtainable.

Further, skewing or diagonal deflection of the frame 24 is stronglyresisted in the provision of the mesh pad structure described and thelateral shape retaining characteristics of the structure are greatlyimproved.

On the other hand, as demonstrated in FIGURES 12 and 13 of the drawingsthe substantially rectilinear configuration of the reaches of the coilspermits some freedom of relative vertical movement between the adjacentcoils. Although the demonstration in FIGURE 13 might be slightlyexaggerated as compared with these relative movements in ordinary use,it does indicate how coils 28a, 28b, 28c and 28d may readily slide invertical directions relatively to each other under certain conditions ofuse, and thus accommodate the cushion to irregularities of the seat orshifting movements of the user.

Now it will be well to describe certain of the important novel featuresof the invention, namely, the trimming of the ends of the coils of thepad and the interconnecting of pairs of twisted ends with the frame 24.

It has already been explained that the respective coils 28 are formed ona mandrel as suggested in FIGURE and immediately moved olf the end ofthe mandrel in threaded interconnected relationship with the lastpreviously formed coil of the mesh being constructed, while of courseupon the completion of each pair of coils 28 the mesh is moved forwardthe width of two coils in the machine. This stage of the construction isclearly shown in FIGURE 5 of the drawings where each successive coil hasbeen threaded to the preceding one; and it will be clearly seen fromthis figure how, when the end of each coil as it comes from the mandrelis severed, a protruding length of wire 30 is left projecting from eachmargin of the web of mesh constituting the area of the pad. It will alsobe seen from this figure that the pairs of crossed flared projectingwire ends 30 are indicated by the brackets as shown, and it is thesepaired ends 30 which are intertwisted to provide the hooked ends whichare interlocked with the frame 24.

In the embodiment of the invention in which the annealing process isemployed, these end projections 30 are subjected to a heating andannealing step intended to render them sufficiently pliable or malleablefor easy intertwining or intertwisting. This annealing may be carriedout through induction heating or in any other convenient manner. Whileit would be thought that the annealed ends would not retain sufiicientstrength and rigidity to permanently interlock with the frame member 24,it has been found that during the actual intertwisting and bending ofthe wires as shown at 35 in FIGURE 3 or suggested at 35 in FIGURE 7,there is produced a cold working of the metal which results insubstantially restoring the hardness within the twisted portions so thatthe resulting united or intertwisted end portions of the coils as at 35may then be readily bent around the rodlike front and rear sections ofthe frame 24 to form rigid hooks, and yet retain their gripping set.

However, a more preferred method of efiectuating the interconnection ofthe ends 30 of the coils 28 does not require an annealing process and isalso effectuated without embrittlement of the wire ends. The wire usedis a low or medium carbon hard-drawn wire and the proper strength andrigidity for attaining a permanent interlock with the frame 24 isattained in the following manner.

From the condition shown in FIGURE 5 of the drawings, rotary twistingdevices seize the diverging pair of projecting ends 30 of the adjacentcoil 28 and by an appropriate camming or other variable drivingmechanism the pitch of the screw of the receding twister progressivelydiminishes: first, a rather long pitch, then a shorter pitch, and astill shorter pitch which provides a gentle start of the twisting actionand avoids crystallizing or overstressing the wire, but applies adelayed tightening action which ultimately results in a fairly uniformtwist in which the wire is not overstressed nor embrittled but retainsthe proper strength and close twist to make an effective permanent jointwith the frame 24. FIGURE 6 constitutes what might be called aninstantaneous view of the twisting of the ends Where the initial portionis somewhat loosely formed and of a rather long pitch as at 31. Fromthis point on, the twisting element moving outwardly at a progressivelydecreasing rate causes the twist of the inward portion 31 to tighten up,at the same time the outward portions are being twisted. The finaleffect of the gradually diminishing outward movement of the twistingelement causes the inner twisted convolutions as at 31 to be tightenedup until the final twist of the paired coil ends 35 is taut and uniformas indicated at 33 in FIGURE 7.

Upon completion of the twisting in preparing the ends 35 for hookingover the frame 24, the projecting barbs 34 comprising the ultimate endsof the wires 30 are snipped off, leaving a clean relatively smooth anduniform end structure 36 of accurately controlled length, for providingthe precisely encircling hook-forming portions 35. This is clearly shownin FIGURE 7; and as a matter of fact, FIGURE 7 constitutes a plan viewof the structure shown in vertical section in FIGURE 3 of the drawingswith the twisted paired coil ends 35 underlying the relatively stiffwire frame 24, perparatory to forming the hooks.

As a final step in the provision of the novel insert pads for thecushions, the intertwisted end portions 35 are bent upwardly around thepreferably cylindrical frame wire structure 24 to substantially encirclethe same as indicated at 40 in FIGURES 2, 3 and 4. The precisely outfree ends of the resulting hooks 40 are disposed within and very closeto the frame structure 24 in near abutting relation with the adjoiningsection of one of the wire coils. This nearly complete encirclement ofthe frame wire 24 by the paired twisted wire end portions as at 40provides complete security against unhooking; and by either methoddescribed herein, the strength of each of these connections issubstantially in excess of any force tending to loosen it in service.

For the purpose of simplicity the orientation terminology in the claimswill be referred to the condition of the seat portion of the cushion,although the claims also cover the corresponding features of the cushionback which is of course adapted to be disposed in a substantiallyupright position in use. Thus the words vertical, horizontal, up, downlateral, etc. are to be considered to cover the features of the backmember, as if the latter were laid out flat in a horizontal position.

It is understood that various changes or alterations may be made in theembodiments disclosed herein, without departing from the scope of theinvention as defined by the following claims.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. The method of making a wire mesh pad which includes the steps ofspirally intertwisting the projecting ends of a pair of adjacentcomponent wire coils, and bending the resulting intertwisted ends arounda marginal frame to substantially encircle the latter, the workingeffected by the subjecting of the coil ends to the intertwisting andbending operations serving to temper and harden the intertwisted ends toeffect a permanent gripping of the frame and without embrittlement.

2. The method as set forth in claim 1 in which the intertwisting stepcomprises applying a progressive rotary intertwisting action to saidends beginning at the base of the convolutions of the coils, which is atfirst of a long pitch resulting in a gentle working, and progressivelyreducing the pitch of said movement, until at the end of the run, theturns of the wire ends are snugly and closely tightened and the endsready for bending without crystallizing or overstressing the wire.

3. The method as set forth in claim 1 in which the Wire is alow-to-medium carbon steel and the intertwisting step comprises applyinga progressive rotary intertwisting action to said ends beginning at thebase of the convolutions of the coils, which is at first of a long pitchresulting in a gentle working, and progressively reducing the pitch ofsaid movement, until at the end of the run, the turns of the wire endsare snugly, closely, and substantially uniformly tightened and the endsready for bending Without crystallizing or overstressing the wire.

4. The method as set forth in claim 1 in which the Wire is alow-to-medium carbon hard-drawn steel and in which the coil ends areannealed to at least partially remove their hardness, the saidintertwisting of the coil ends serving to restore sufficient of theoriginal hardness of the wire ends to effect a secure grip when they arebent around said frame.

5, The method as set forth in claim 1 in which releasing of the wireends at the end of the intertwisting step results in projecting barbs,and thus the steps are included of References Cited UNITED STATESPATENTS 3,348,583 10/1967 Goldmeyer et a1 140-3 FOREIGN PATENTS 167,7375/ 1956 Australia.

CHARLES W. LANHAM, Primary Examiner. LOWELL A. LARSON, AssistantExaminer.

U.S. C1.X.R. 29-160; 140-107, 149

